1. Testing General Relativity Hyperspace, Wormholes, and Warp Drives

2. We’ve seen that GR describes gravity as masses warping spacetime, and other masses moving in as straight a line as possible through that warped space Interesting idea – but is it real? Is there any evidence supporting this weirdness?

3. Precession of Mercury’s Orbit 43 seconds too much, according to Newton’s model of gravity Mercury’s orbit precesses. The semimajor axis revolves around the Sun just a little faster than Newton’s laws can account for. Einstein’s general relativity predicts the excess exactly.

4. Stars near the Sun appear to move “Warped spacetime” suggests that starlight should also follow a bent path. Light has no mass, and so Newton’s laws predict it is not affected by gravity. But in fact, starlight is bent when it travels near a large mass like the Sun.

6. Gravitational Lensing The right geometry should allow that bending to create multiple images of a distant object…

7. Einstein rings Einstein cross Warping by a galaxy cluster

8. Gravitational Time Dilation – time runs slower in a stronger gravitational field Radar signals bounced off Venus or Mercury just before or after occultation show time dilation GPS satellite clocks are adjusted to account for both special and general relativistic effects Specific atomic transition frequencies were compared between the attic and the basement of this science building at Harvard. Gravitational redshift has been observed in light from our Sun and other stars

9. As two neutron stars in a close binary pair orbit each other, relativity predicts they should radiate away energy in the form of “gravitational waves”. Data gathered since 1974 shows the decrease in orbital period of just such a pair. It agrees with relativity’s prediction extremely well. Gravitational Waves

10. LIGO, Hanford, WA, showing 4 km long arms “Laser Interferometer Gravitational-wave Observatory” Right now light is all we have from the stars and galaxies. That may soon change.

11. The “Twin Paradox” Tim and Jim are twins. Tim boards a spaceship and travels to Vega, 25 ly away, and back at 0.995c. 50 years goes by for Jim before Tim returns. Meanwhile, Jim observes Tim’s clocks moving slower than his own, so he says Tim is aging slower.

12. The “Twin Paradox” Tim and Jim are twins. Tim boards a spaceship and travels to Vega, 25 ly away, and back at 0.995c. 50 years goes by for Jim before Tim returns. But Jim observes Tim’s clocks moving slower than his own, so he thinks Tim is aging slower. On the other hand, Tim sees Jim moving, and would say that Jim is aging slower. When Tim returns, which one will really be younger?

13. The “Twin Paradox” Upon Tim’s return, the twins find that Jim has aged 50 years while Tim has only aged 5 years. How can we say this for sure? What’s the real difference between their reference frames? Acceleration Also,…

14. The “Twin Paradox” From Tim’s perspective, it’s the universe that’s moving at 0.995c, so he sees the distance from Earth to Vega shrink to 2.5 ly. According to Tim’s clocks only 5 years go by for the whole trip. 2.5 ly 0.995c

15. Hyperspace, Worm Holes, and Warp Drive A trip from Brazil to Indonesia is about 20,000 km around the surface of the Earth If you could go through a tunnel through the center of the Earth, the trip would only be 12,800 km 8

16. Hyperspace, Worm Holes, and Warp Drive In the same way, since the 4-dimensional spacetime of our universe is curved, it’s possible that in some places a shortcut could exist through a fifth dimension – hyperspace – that would make our trip much shorter. This is called a wormhole. GR does NOT say that these exist. But it doesn’t say that they can’t exist. Remember that we’re talking about warped spacetime, so being able to jump through hyperspace to other places implies an ability to jump to other times. Most physicists believe that time travel will one day be proven to be impossible, due to serious paradoxes that it involves.

17. Hyperspace, Worm Holes, and Warp Drive However, until it’s proven impossible, it remains a possibility that science fiction writers love to make use of. “Warp Drive”?

18. Astro-Cash Cab! Pauline Merlin Tabitha Connor J.

19. 1) What evidence been found that the predictions of general relativity are true? a)We've seen gravitational lensing caused by the Sun, stars, and galaxies. b)The spectrum of white dwarf stars shows a redshift due to time slowing down. c)The perihelion of Mercury's orbit precesses according to general relativity. d)all of the above e)A and C

20. 2) Are there such things as gravitational waves? a)Yes, they are like electromagnetic waves except made by accelerating masses rather than accelerating charges. b)Yes, they are ripples in spacetime c)No, we have never seen evidence of them, although they are theorized to exist. d)A and B e)none of the above

21. 3) True or False? When one of a pair of twins travels near the speed of light and then returns to Earth, the traveling twin and the twin on Earth both agree that the traveling twin is the older of the two.

22. 4) True or False? Einstein’s General Theory of Relativity predicts / explains the existence of Einstein Rings.